I've written a lot about this question already, but let me add a few things.

Assuming an outsider position in order to defend what we think is true is incumbent on everyone on every issue. It's the attempt to be as objective as humanly possible with regard to our disagreements. It's to have a disinterest in the outcome as best as possible.

But it applies more forcefully to religious faiths, that's why it's called what it is. Why? Because religious believers do not dispassionately evaluate their faith. Why? Because they have such a vested personal interest in defending what they believe. Why? Because they assume what needs to be proved. Why? Because they do not have any good evidence for them. Why? Because they amass many possible arguments together in a pile then conclude they have a probable case, which is a huge non-sequitur.

By contrast atheism is not about faith. I think I explained that in my chapter for The Christian Delusion. Atheism is based on the probabilities. And I explained there is little or nothing we can know about an atheist simply because he is an atheist, except that said person does not believe in supernatural beings and forces, nor does he think supernatural explanations have the weight of evidence for them.

The sciences are the paragon for outsiders. Show me the math and we agree. Show me the experiment and the argument is over. Show me the scientific poll and the case is closed. Show me what we learn from brain science and there can be no dispute.

Is this a double standard, one for religious faiths and another one for atheists? No! Religious people have the double standard. Why do they evaluate other religious faiths with a level of skepticism that they do not apply to their own culturally inherited one? Why? Answer me that! The OTF is a way to examine all religious faiths. If this is a bad test then how do Christians propose we decide between religious faiths? I’ve proposed the OTF. What’s the alternative? Answer this question too.

So let’s contrast this carefully and precisely. Can theists legitimately say that if I do not collect stamps I still have a hobby? How does that make sense? Let’s say someone tells me I believe in the supernatural realm even though I don’t believe in ghosts? Now let’s say someone asks me to subject my non-ghost view to the skepticism of an outsider. What can that possibly mean? I DO subject the ghost view to skepticism, that’s why I conclude there are no ghosts!

Is it enough to ask people to be objective, fair, and openminded? I've previously addressed this question but let me add that if human beings reason so badly that we implicitly adopt what we were taught to believe in our respective cultures so much that they become like blinders on our eyes, and if we’re that bad at weighing the claims of beliefs that have little or no evidence for them to decide between differing ones, then we cannot offer a milquetoast test that asks people to be objective, fair and openminded about that which they were raised to believe and defend. What we are enculturated with is who we are. We cannot see the water we swim in. We cannot pluck our eyes out and look at them. So we cannot simply ask people to be objective, fair and openminded. Believers already think they are being objective because they can't see that they are not! Just look at how confident some Muslims are that they are being objective. Some of them are so certain they're objective about their faith they are willing to fly planes into buildings. Ask them if they’re objective and it would be a no brainer for them. But ask them to subject their own faith to the same level of skepticism they use to reject other faiths and THAT will get their attention. Since we cannot pluck out their eyes we must offer them a shocking test, one that may help get them out of their dogmatic slumbers like nothing else can do. And they will object as strenuously as they can to the OTF because they know their faith does not pass that test. That’s why Christians argue against it just like Muslim scholars would do so for their faith.

What about people raised as atheists in Sweden? Were they enculturalted? Probably so.

Should these atheists test what they were taught by being objective, fair and openminded? Sure, yes.

Should they test what they were taught as outsiders? How can they? What is the outside perspective for them? Is it the perspective of a young earth Christian creationist or a young earth Jewish orthodox perspective? Any scientist would scoff at it because science produces repeatable evidence that convinces. Is the outside perspective that of a Wiccan, or a Scientologist? How can atheists choose the correct outsider perspective from the many available? Which religious perspective do objectors to the OTF propose we use when being outsiders?

The OTF is a reasonable fair and objective one to judge religious faiths. The whole reason Christians object to it is because they know their faith will not pass the test, even if they admit no other religious faith can do so either. So cognitive dissonance requires them to nitpick at it and point out any small loophole to avoid taking it, even though this is how they judge the other faiths they reject. THEY have the double standard.

So on the front side of the fence, the fact that no revealed religion can pass this test is not the fault of the test. Again, it's a reasonable, fair and objective one. If no revealed religion can pass the OTF then it's the fault of religious faiths, not the test. It means they cannot be justified.

On the back side of the fence, there is no worthy religious contender from out of the myriad number of religions for an atheist to examine his own views on religion as an outsider. But that is not the fault of the test either. The fact that there isn't one religion that succeeds in being the one lone contender over all of the other religions as the rightful outsider position from which to judge my atheist conclusions about religion is not the fault of the test itself. They cannot put up one and only one religion which they all agree would be an outsider's perspective for the atheist. Again the test is a fair and objective one. The fault is with religious faith.

As I said I see no reason why a religion could not pass this test. A religion could pass the test. The fact that no religion can pass the test is not the fault of the test. The test is a reasonable, fair and objective one. Whether on this side of the fence or the back side of it, the fact that Christians object to the test because no revealed religion can pass it on the one side, and that there is no worthy religion that can legitimately be considered as an outside perspective for the atheist, is not the fault of the test.